The present invention relates to a laser irradiation system for irradiating laser beam by rotary irradiation and for forming a reference plane by the laser beam.
A laser irradiation system is used for irradiating the laser beam by rotary irradiation to a plane, which is regarded as a reference, and for forming a reference plane by the laser beam. When the laser beam scans across an object such as a wall surface, a locus of the laser beam serves as a reference line on the reference plane. Therefore, when the reference plane is a horizontal plane, the reference line runs in a horizontal direction, and the height of the reference line is equal to the height of the reference plane. Thus, the reference line is used as a reference for horizontality or height.
Visible light or invisible light is used as the laser beam irradiated from a laser irradiation system. In case visible light is used, the maximum output of the laser beam is restricted in order to ensure safety of the personnel such as operator. For this reason, in a laser irradiation system using visible light beam, stationary irradiation is performed toward a predetermined point or reciprocal scanning is performed within a predetermined range around a predetermined point in order to increase apparent luminance and to improve visibility and to facilitate visual confirmation. In some cases, there is provided a target for determining the predetermined point, and the laser irradiation system comprises the target and a rotary irradiation system main unit for irradiating the laser beam. The rotary irradiation system main unit used in this type of laser irradiation system has a function to detect the target, and the rotary irradiation system main unit is provided with a photodetection unit for detecting the reflection light beam from the target. The photodetection unit detects the reflection beam from the target and the position of the target is detected according to the result of the detection by the photodetection unit.
Description will be given below on a conventional type rotary irradiation system main unit 1 and a target 2 referring to FIG. 13 and FIG. 14.
The rotary irradiation system main unit 1 comprises a light emitter 5, a rotator 6, a photodetection unit 7, a control unit (CPU) 8, a light-emitting element driving unit 9, and a scanning motor driving unit 10.
First, the light emitter 5 will be described.
On an optical axis of a laser diode 11, which emits a laser beam 20, there are provided a collimator lens 12 and a perforated mirror 13 in this order as seen from the laser diode 11. The laser beam 20 emitted from the laser diode 11 is turned to parallel beams by the collimator lens 12, and the beams pass through the perforated mirror (or half-mirror) 13 and are projected toward the rotator 6.
The rotator 6 deflects the optical axis of the incident laser beam 20 coming from the light emitter 5 by 90.degree. and projects the beam in a horizontal direction and further rotates it. The optical axis of the laser beam 20 coming from the light emitter 5 is deflected by an angle of 90.degree. by means of a pentagonal prism 14. The pentagonal prism 14 is mounted on a rotation support 15, which is rotated around the optical axis of the light emitter 5. The rotation support 15 is connected to a scanning motor 18 via a scanning gear 16 and a driving gear 17. Rotating condition of the rotation support 15 is detected by an encoder 19 mounted on the rotation support 15, and a detection signal of the encoder 19 is inputted to the control unit (CPU) 8.
It is designed in such manner that a reflection laser beam 20' from the target 2 enters the rotator 6. When entering the pentagonal prism 14, the reflection laser beam 20' is deflected toward the perforated mirror 13, and the perforated mirror 13 reflects the reflection laser beam 20' toward the photodetection unit 7.
Next, the photodetection unit 7 will be described.
On a reflection optical axis of the perforated mirror 13, there are provided a condenser lens 21 and a photodetection element 22 in this order as seen from the perforated mirror 13, and photodetection status is outputted from the photodetection element 22 to a reflection light detecting unit 23, which is to be described below.
The reflection light detecting unit 23 detects the photodetection status of the reflection laser beam 20', i.e. the reflection status of the laser beam 20 at the target 2, and the detection status is outputted to the control unit 8. Now, description will be given on the control unit 8.
Signals from the encoder 19 and the reflection light detecting unit 23 are inputted to the control unit 8.
The control unit 8 drives the light-emitting element driving unit 9 and emits the laser beam 20. Further, it controls the scanning motor driving unit 10 based on the signal from the reflection light detecting unit 23. Based on the control signal from the control unit 8, the scanning motor driving unit 10 drives the scanning motor 18 and rotates the pentagonal prism 14 via the driving gear 17, the scanning gear 16, and the rotation support 15. Rotation status and rotating position of the pentagonal prism 14 are detected at the control unit 8 as the signal from the encoder 19 is fed back to the control unit 8. When the pentagonal prism 14 is rotated while the laser beam 20 is being emitted from the laser diode 11, the laser beam 20 projected in a horizontal direction is rotated, and a reference plane is formed by the laser beam 20.
The target 2 has a reflection surface, by which the target 2 is recognized as the target 2 when the laser beam 20 scans across the target 2, or/and by which it is possible to detect the center of the target 2. In the following, description will be given on the target 2 referring to FIG. 14(A) and FIG. 14(B).
Reflection layers 26 and 27 are provided on each of a base plate 25 respectively, and there is a non-reflection surface between the reflection layers 26 and 27. The reflection layer 27 reflects the laser beam 20 projected from the rotator 6 so that the laser beam 20 enters the rotatorc 6 again. Because there are provided two reflection layers, when the laser beam 20 scans across the target 2 as shown In FIG. 14(A), the reflection laser beam 20' from the target 2 is turned to two pulse-like forms with the middle portion lacking as shown in FIG. 14(B). Therefore, it is possible to identify the target 2 from the photodetection result.
After the target 2 was detected, the rotary irradiation system main unit 1 projects the laser beam 20 by reciprocal scanning within a predetermined range around the target 2.
In recent years, the scope of application of the laser irradiation system has been widened, and it is often necessary now to identify a target at a remote place. As described above, however, there is restriction on the maximum output of the laser beam. Accordingly, in order to identify a target at a remote place, the photodetection amount (light quantity) should be increased without loss. One of the means to increase the photodetection amount is to increase the size of the perforated mirror 13 of the photodetection system. This causes such problems that the optical system including the pentagonal prism 14 must be designed in larger size or that a driving system relating to the optical system must be designed larger.